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It’s still dangerous though. Cost of a 12V power supply vs a small chance of killing myself, I’d spend the money. 3D printers aren’t cheap anyway, why economise on safety?

When choosing an appropriate MOV for a specific overvoltage-protection application, the circuit designer must first determine the operating parameters of the circuit being protected, including:

I’ve spent four to eight years in apprentice school learning how to plan, install, inspect, and repair electrical products. Don’t insult my intelligence by implying otherwise.

I learned even more respect for shock hazards on the job one day when I was working for a military contractor. I forgot to turn off the 400VDC B+ supply to a radar driver assembly before I put one hand on the metal chassis and grabbed the fins of a lighthouse tube with the other hand. After that I put my head down on the workbench and had me a rest for a few minutes. Even when you know better, one moment of inattention can be the end.

For something like this I would go to a proper electrical supplier and probably would use an AC contactor relay that’s rated twice the current. Sure a contactor needs a 24V transformer but it’s a small price to pay and the current use would be insignificant compared the the hot water heater.

The dimmer switch for the kitchen lights was rated for up to 600 watts, but the wattage at the lights was more than this; there were ten 65-watt bulbs on this circuit. This caused the front of the switch to get extremely hot, and creates a potential fire hazard. Have this corrected.

When a circuit breaker has a lot of current flowing through it, it will get warm. The warm 15-amp circuit breaker shown below had a 15.6-amp hair dryer running for about 20 minutes, and it warmed up to about 17 degrees over ambient. It wasn’t especially hot, but it was definitely overloaded.

My first job in the trades was as an electrician’s apprentice doing tasks, such as pulling wire, building light fixtures, and moving scaffolding in grocery store renovations. I moved into HVACR and now serve as an HVACR contractor, instructor, and electrician.

And keep in mind that EVSEs are a continuous duty device. As such, you need to derate them from the circuit’s rating by 20%. So you should only use 12A on a 15A rated circuit. And you should only do that if you’re confident that there’s nothing else pulling significant current on EITHER circuit besides your EVSE.

So, you agree with 3mm. Good. A step forward. And because I see you want to use that Industrial standard as example how is your standard looking in case of soldermasked and conformal coated board? What I can say is that I used the 3mm/kV rule and never failed me in 25 years, no board rejected ever…and for the sake of the discution, as you know, when we are under 500V/10A circuits things looks a bit different in PCB Design. We are not sending nobody to the Moon nor switching a 500A Engine starter. It’s a max 300W lighbulb Switch and it’s 99.99% safer than the latest zilions of made in China dimmers and fake USB SMPS Mobile Chargers that arrived in your city in the last month.

Heck, as I said, when I have needed to do this in the past I just used a multimeter, a terminal block, and no relaying whatsoever (ah, being perhaps complacent “qualified personnel”, eh?)